While it may seem like Linux-only projects are betraying their loyal base by developing Windows or OSX versions, I would argue that cross-platform development is actually better for Linux as a whole, better for individual software projects and their developers, and ultimately better for Linux users.

I work developing software for companies out there, I mostly work on Linux, but my coworkers use a mix of Linux and other UNIX-like OS. You couldn't imagine how many companies out there ask their employees not to develop software on Windows.